The increasing complexity and cost of various spacecraft and associated launch and ground systems therefore have created a need for extensive detailed validation and verification before deployment along with rigorous training for support personnel from booster separation to satellite end of life. Examples of systems contributing to the need for extensive testing and training include: (i) multiprocessor-based systems which can have complex software architectures; (ii) multiple launch systems with various delivery characteristics and mission requirements; (iii) multiple ranging systems used to support mission and on-going operations; (iv) ground systems with multiple interacting elements; and (v) sophisticated ground software for automated spacecraft operations.
However, system-level ground testing to verify full system performance of a spacecraft and associated systems as well as a realistic training environment for support personnel can be costly and/or inadequate. Present implementations of hardware-in-the-loop systems to provide ground testing require special purpose interface hardware, software and harnessing to create a test environment whereby system hardware or emulations thereof can be integrated with high-fidelity, real-time simulations and then instrumented to facilitate testing and training.
As the spacecraft orbits the earth multiple ground stations are used to provide ranging vectors that provide real time information such as range, azimuth and elevation data of the spacecraft. As the satellite moves around the earth different ground stations and thus different ranging and tracking systems can monitor the spacecraft and generate ranging, azimuth and elevation data. The functions of the ranging and tracking systems are particularly important when the spacecraft is first launched into a transfer orbit and precise position data is required to efficiently and safely move the satellite from the transfer orbit into its final orbit. Then too, during normal operations, efficient station keeping is dependent upon the precise knowledge of spacecraft position. Turnaround ranging is typically used whereby two or more ground stations are used to improve the determination of spacecraft position. Thus, there is a need to simulate the operation of various ranging and antenna systems at various times to provide a complete simulation of the system. Prior efforts for simulating different ground stations include using different simulators for each of the ranging and antenna systems throughout the world that are to be used for a specific mission. However, such an approach is extremely costly due to the great number of simulators required. Also, systems that implement a separate machine to represent each ground station ranging mechanism require a complex exchange of ephemeris or ranging information with corresponding complexities related to time tagging of information. Inaccuracies of only a few milliseconds in these systems will result in invalid ranging results and comprise testing results. Another type of system modifies internal geographic references on a scheduled basis to match the ranging and tracking schedule in the ground control software. Sharing scheduling information creates considerable complexity and substantial modifications to the ground station software that then propagates to the simulation system. Limitations of the system may compromise the flexibility of the operational ground system design.
It would therefore be desirable to provide a single simulation system that allows multiple ground stations to be simulated accurately with respect to time.